Field of the Invention
The present invention relates to a sheet-stapling apparatus that staples center-folded booklet (sheets) by staple(s) and an image-forming system that uses such a sheet-stapling apparatus.
Description of Related Art
A technology to staple a bundle of sheets by a staple has been known in the past. In order that the staple 55 penetrates through a sheet 10P, the staple 55 may have to shear a part of the sheet 10P as shown in FIG. 1A or to rupture a part of sheet 10P with fibers of the sheet 10P being extended as shown in FIG. 1B.
In both cases, the part of the sheet 10P sags by the staple 55 and when exceeding an allowable sagging amount thereof, the part of the sheet 10P opens for the staple 55 to penetrate through the sheet 10P. When increasing number of the sheets 10P, it is difficult for the staple 55 to penetrate through the sheets 10P because an apparent thickness of the sheets 10P is increased by the sag of the sheets 10P.
As shown in FIGS. 2A through 2C, it is known that so-called glasses type clinch in which legs of the staple are curled while the legs of the staple are still curved has performed to form a booklet. In this case, a clincher 50 mounts the booklet 10 in which plural sheets are bundled. Clincher 50 has a narrow cut 51 that allows the legs of the staple 55 to be curled.
A driver 52 drives the staple 55 so that the legs of the staple 55 penetrate through the booklet 10 as shown in FIG. 2A. The driver 52 further drives the staple 55 so that the legs of the staple 55 which penetrates through the booklet 10 are conducted to the narrow cut 51 of the clincher 50 as shown in FIG. 2B and that the legs of the staple 55 are bent inwardly as shown in FIG. 2C.
A sheet-stapling apparatus that staples center-folded booklet (sheets) by staple(s) has been proposed in the past as a sheet finisher for performing any staple processing on the sheets, and the like (see Japanese Patent Application Publication No. 2010-150002). It has been known that it is desirable to align a fold of each of the sheets with a position to be stapled by the staple when the sheet-stapling apparatus forms the booklet by stapling it using the staple(s).
Accordingly, a technology to perform any stapling processing on the center-folded booklet after the booklet is mounted has been known. As shown in FIG. 3A, when the driver drives the staple 55 so that the legs of the staple 55 penetrate through the fold 10a of the center-folded booklet 10, an amount of work to be done in order that the booklet 10 sags beyond the allowable sagging amount by the staple 55 is larger than that done by the staple 55 in a case where the legs of the staple 55 penetrate through a flat part of the booklet 10 as shown in FIG. 3B. Accordingly, it is difficult for the staple 55 to penetrate through the booklet without any buckling of the staple. Normally, as shown in FIG. 3C, by allowing the booklet 10 to sag, it may be easy for the staple 55 to penetrate through the booklet 10, which prevents the buckling of the staple 55.
In the past, as shown in FIG. 4, in order to clear up a difficulty for the staple to penetrate through the booklet, the staple processing has been performed after a pushing member 60 has pushed the booklet 10 to a supporting member 61 in order to make a fold of a portion of the booklet to be stapled flat.